Significantly enhanced CO2 capture properties by synergy of zinc ion and sulfonate in Pebax-pitch hybrid membranes

Abstract

For high-performance hybrid membranes, it is crucial to design multi-functional filler to rationally manipulate the structure-property relationship. In this study, a novel kind of hybrid membrane was fabricated by incorporating zinc ion loaded sulfonated pitch (SP-Zn2+) nanofillers into poly (ether-block-amide) (Pebax) matrix for CO2/CH4 separation. Sulfonated pitch (SP) with high sulfonate content was functionalized by zinc ion (Zn2+) via complexation reaction to synthesize SP-Zn2+ nanofillers with high Zn2+ loading. Mixed gas separation performances of membranes with different SP-Zn2+ loading were conducted. Meanwhile, the effect of operating pressure on separation performance and long-term operation stability were investigated. The hybrid membranes displayed significantly enhanced permeability and CO2/CH4 selectivity. First, the hydrophilic sulfonate group in SP had good compatibility with Pebax matrix and effectively suppressed interfacial defects. Second, zinc ions and sulfonate group could form zinc-sulfonate complex network. The sulfonated moiety afforded strong affinity toward CO2 due to multiple interactions whereas the Zn2+ moiety afforded a transport highway for CO2. Third, the incorporation of SP-Zn2+ nanofillers could disturb the Pebax chain packing and optimize the free volume characteristics. Particularly, Pebax/SP-Zn2+(2) membrane exhibited an increment of 104% and 70.2% in CO2 permeability and CO2/CH4 selectivity respectively, much higher than that of Pebax membrane.